Process of producing 2,6-dimethylnaphthalene by dehydrocyclizing 1-(p-tolyl)-2-methylbutane and/or 1-(p-toly)-2-methylbutene using a reduced vanadium catalyst

ABSTRACT

The invention concerns a preparation process for 2,6-dimethylnaphthalene in which 1-(p-tolyl)-2-methylbutane and/or 1-(p-tolyl)-2-methylbutene are dehydrocyclisized using a reduced vanadium catalyst. 2,6-dimethylnaphthalene can be used as starting material when manufacturing polyethylenenaphthalate. The conversion of this method is good and the selectivity of 2,6-dimethylnaphthalene can be improved by reducing the catalyst.

FIELD OF THE TECHNOLOGY

The invention concerns a process for the preparation of2,6-dimethylnaphthalene in which 1-p-tolyl)-2-methylbutane and/or1-(p-tolyl)-2-methylbutene are dehydro-cyclisized using a catalyst.2,6-dimethylnaphthalene can be used as a starting material when makingpolyethylenenaphthalate.

BACKGROUND OF THE TECHNOLOGY

Polyethylenenaphthalate has very good stress- and heat-resistance. Itsknown preparation processes, however, have not been industriallyprofitable.

Polyethylenenaphthalate can be made from 2,6-naphthalenedicarboxylicacid which in turn can be made from 2,6 dimethylnaphthalene. Nowadays2,6 dimethyl-naplthalene is separated from tar. However, in this wayonly small amounts can be obtained. Furthermore, the separation andpurification are troublesome.

It has also been suggested that 2,6-dimethylnaphthalene is made from1-(p-tolyl)-2-methylbutane and/or 1-(p-tolyl)-2-methylbutene bycyclization using different catalysts. The problem has especially beenthat in the reaction one obtains big amounts of different isomers, whichare difficult to separate. Furthermore, the starting material easilypolymerizes and degrades.

For instance, in the publication GB 1448136 there has been described thepreparation of 1-tolyl)-2-methylbutane and/or 1(p-tolyl)-2-methylbuteneusing a Cr₂ O_(3/) Al₂ O₃ -catalyst which has been poisoned bypotassium. In the publication EP 430714 a catalyst composed of lead-and/or indium-oxide together with aluminium-oxide has been proposed.

A General Description of the Invention

Now a process according to claim 1 has been invented. Some advantageousapplications of the invention are presented in the other claims.

According to the invention, 2,6-dimethylnaphthalene is made from1-(p-tolyl)-2-methylbutane and/or 1-(p-tolyl)-2-methylbutene using areduced vanadium catalyst. For instance, the conversion of the processis good compared to chromium catalysts, and especially the selectivityof 2,6-dimethylnaphthalene can be improved by reduction of the catalyst.Also the environmental risks for the vanadium catalyst can be consideredsmaller than for the chromium- and lead-catalysts.

A Detailed Description of the Invention

The vanadium catalyst used in the invention can be made using anysuitable method for applying vanadium on a support. One can, forinstance, use the methods of wet-or dry-impregnation or adsorption orprecipitation. Among the dry-impregnation methods especially the co- andmulti-impregnations provide good results both regarding the reaction andthe phase transitions of the support material. After the impregnation,adsorption or precipitation the catalyst is dried at 120° C. andcalcinated. The calcination is carried out in an oxidizing atmosphere,especially in air, in a temperature range of 300-800° C.

The preferred vanadium content is 1-15 wt-%, preferably 2-5 wt-%,calculated as vanadium per total weight of the catalyst. In thepreparation the preferred vanadium source can be a water solublevanadium compound like ammonium vanadate. The solubility of ammoniumvanadate can be improved by adding oxalic acid to the impregnationsolution.

The catalyst can also contain one or several modifying components.Suitable modifying components are especially the earth alkali metals,most favourably calcium and strontium, as well as the metals of theelementary group IV A, for instance zirconium. Also the sources of themodifying components can be water soluble compounds like nitrates. Themolar ratio of vanadium and the modifying component should be below 4 inthe case of earth alkali metals and below 2 in the case of group IV Ametals.

Any suitable material can be used as a support. For this purposeespecially γ-, θ- or δ-aluminum oxides with a specific surface area of50-400 m² /g are suitable. Before vanadium is impregnated on the supportone can thermally stabilize the support. The modifying agent can beimpregnated on the support before or after the stabilization.

The catalyst can be reduced in a suitable way especially by contactingit with a reducing gas phase like carbon monoxide or hydrogen. Asuitable inert gas like nitrogen can be used for dilution. Thecontacting temperature can be for instance 400-700° C. and thecontacting time 0.1-120 min. After the treatment the reducing gas isremoved from the catalyst by flushing with a suitable gas like nitrogen.

The treatment of a vanadium oxide catalyst with carbon monoxide forammoxidation of aromatic hydrocarbons is known from the publication U.S.Pat. No. 3,901,933. By this treatment one has tried to improve theactivity of the catalyst in the reaction mentioned above.

The preparation of 2,6-dimethylnaphthalene according to the invention isdone by contacting 1-(p-tolyl)-2-methylbutane and/or1-(p-tolyl)-2-methylbutene under dehydrocyclization conditions with acatalyst which has been made as described above. As reaction temperatureone can use 350-700° C., preferably 450-600° C. The reaction can be doneat any pressure, for instance, in the range 0.1-5 bar. In addition to1-(p-tolyl)-2-methylbutane and/or 1-(p-tolyl)-2-methylbutene one canfeed to the reactor a diluent gas like, for instance, nitrogen or watervapour.

EXAMPLE 1

A carrier was made by crushing (0.5-1 mm) γ-aluminium oxide (surfacearea about 200 m² /g, porosity 1.2 ml/g) and precalcinating at 750° C.for 16 h. Onto the carrier one co-impregnated a water solution ofammoniumvanadate [NH₄ VO₃ ] and oxalic acid [(COOH)₂ * 2H₂ O][the molarratio of NH₄ VO₃ and (COOH)₂ * 2H₂ O was 0.5] as well as water solutionprepared from calcium nitrate [V/Ca molar ratio was 3]. The catalyst wasaged for 1 h at room temperature, dried for 4 h at 120° C. andcalcinated for 2 h at 700° C. (the temperature increase was 2° C./min).The vanadium content of the catalyst was 5 wt-%, and the aluminium oxidewas still in the γ-form.

2.15 g (4 ml) of the catalyst prepared as presented above was put into aglass tube reactor. In the first experiment 97%1-(p-tolyl)-2-methylbutane was fed to the reactor at an LHSV of 0.48 h⁻¹using nitrogen as a carrier gas [N_(2:1)-(p-tolyl)-2-(methylbutane)=1.9]. The reaction took place underatmospheric pressure at 510° C. and the contact time was 3.9 s. In thesecond experiment the catalyst was reduced before the reaction withhydrogen at 650° C. (20 ml/min, 15 min) and in the third experiment withcarbon monoxide at 650° C. (20 ml/min, 15 min). After the reduction andbefore starting the reaction the catalyst was flushed with nitrogen. Foreach experiment the sample was taken 60 min after starting theexperiment. The results are presented in the table below.

    ______________________________________                                                             V/Ca/Al.sub.2 O.sub.3                                                                   V/Ca/Al.sub.2 O.sub.3                            V/Ca/Al.sub.2 O.sub.3 H.sub.2 -red. CO-red.                                 ______________________________________                                        Conversion (C) 69.4      65.8      63.6                                         C.sub.6 -C.sub.11 42.2 45.5 42.0                                              2-methylnaphthalene 0.7 0.7 0.9                                               1-(p-tolyl)-2-methylbutenes 10.2 13.2 14.1                                    C.sub.12 -alkyl-indanes 1.0 0.9 0.9                                           C.sub.12 -alkyl-indenes 9.8 7.4 7.3                                           Dimethylnaphthalenes 29.7 26.0 30.1                                           (as 2,6-dimethylnaphthalene) 26.2 24.0 27.7                                 ______________________________________                                    

According to the results, the portion of dimethylnaphthalenes which isas 2,6-dimethylnaphthalene increases when the catalyst has beenpre-reduced. Furthermore, the reduced catalysts achieve a betterselectivity level more rapidly after starting the experiment as comparedto a non-reduced catalyst.

EXAMPLE 2

Onto the pre-calcinated support made in Example 1 zirconium nitrate(starting material ZrO(NO₃)₂ * H₂ O) was dry-impregnated. Then it wasaged for 1 h and dried at 120° C. for 4 h after which it was impregnatedwith an ammonium vanadate-oxalic acid-solution according to Example 1.Then it was aged for 1 h and dried and calcinated as in Example 1. Thevanadium content of the catalyst was 2.6 wt-%, the V/Zr-molar ratio 1and the aluminium oxide was in the γ-form. The catalyst can be reducedand used in the reaction as in Example 1.

What is claimed is:
 1. Process for preparing 2,6-dimethylnaphthalene,comprising dehydrocyclizing 1-(p-tolyl)-2-methylbutane and/or1-(p-tolyl)-2-methylbutene using a reduced vanadium catalyst.
 2. Processaccording to claim 1, wherein the catalyst is attached to a solidsupport.
 3. Process according to claim 1, wherein the vanadiumconcentration in the catalyst is 1-15 wt-%.
 4. Process according claim1, wherein the catalyst additionally contains a modifier.
 5. Processaccording to claim 4, wherein the modifier is calcium.
 6. Processaccording to claim 1, wherein the catalyst is reduced using a reducinggas.
 7. Process according to claim 6, wherein the catalyst has beenreduced in a carbon monoxide containing atmosphere.
 8. Process accordingto claim 6, wherein the catalyst has been reduced by hydrogen. 9.Process according to claim 6, wherein the catalyst has been reduced bycontacting it with a reducing gas at 450-700° C. for 0.1-120 min. 10.Process according to claim 2, wherein the solid support is γ, θ- orδ-aluminium oxide.
 11. Process according to claim 4, wherein themodifier is an earth alkali metal.
 12. Process according to claim 4,wherein the modifier is a group IVA metal.
 13. Process according toclaim 12, wherein the group IVA metal is zirconium.